Get rid of outbuilding (4)
I believe the answer is:
shed
I believe this clue is a double definition.
'get rid' is the first definition.
(shed can mean to get rid of or discard)
'outbuilding' is the second definition.
(outbuilding in a garden)
'of' is the link.
(Other definitions for shed that I've seen before include "Discarded" , "One-storeyed outbuilding" , "storage building" , "warehouse" , "Lose or take off in small building" .)